What does petroleum geology study?

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Greetings friends and members of the steem platform.

Logically we know that geology is a science that studies the earth's surface in its physical form, however this has a very broad sense, which is why there must be a ramification of different disciplines for geology. For the case of this article I am going to explain exactly what petroleum geology studies and other associated generalities.

Taking into consideration the previously explained, it is necessary to assume petroleum geology as a branch of geology that studies all the existing forms in which could have been formed the reservoirs containing not only oil but also natural gas, these reservoirs are called by the technical petroleum literature as oil reservoirs.

Petroleum geology is not so limited and provides engineering with a range of possibilities when contributing to the area of study, since it can extend its studies beyond the formation of oil reservoirs, for example, it can study the prospective capacity of an oil field to contribute and produce oil during its useful life through the geological data obtained in the exploration process of the area under study.

Objectives of the study of petroleum geology

1. Location of possible deposits:

When reference is made to possible deposits is because in spite of all the geological studies that are made, they will cease to be possible until a well is drilled within the field that houses the oil reservoir or reservoirs and the precious liquid (oil) is found, otherwise until this activity of drilling wells is not performed there will be no certainty that there is oil in a given area, however these geological studies provide a high possibility of selecting a location where oil is found.

If we talk about the application of techniques within petroleum geology, it must be said that this discipline has several methods and techniques that maximize the percentage of success in finding oil, in such exploratory activities should allow the application of any technique as long as it is of low environmental impact, low cost and finally that such technique manages to collect the best petrophysical data to be delivered to the engineers who will be in charge of the exploratory drilling project.

2. Characterize the spatial geometry and the estimation of its potential reserves:

For this case, even when there is 100% certainty that the oil field has oil, petroleum geology should not limit its contribution until that point is reached, since there is still the need to know the size of the reservoir, and this is only achieved with a characterization through reservoir simulation, and this is where petroleum geology has an important contribution.

Once the type of crude oil is known and with all the geological information, the oil reserves of the reservoirs that will make a contribution of those reserves that in the end are considered potential, since they can have high oil flow rates in their future production, can be estimated.

Pre-drilling exploration

Several technical studies are carried out before drilling an exploratory well in the area, including the study of geological maps, study of geophysical methods such as gravimetry and electrical soundings.

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For the realization of these maps it is important to see the dedication of geologists collecting information on the surface, information that is of great relevance for the elaboration of the maps.

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Within these studies perhaps many of you have heard of seismography studies where basically the telluric movements generated intentionally in the subsoil are measured to obtain some results that are convincing to get an idea of whether there really is hydrocarbon in the study area.

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What does petroleum geology look for with pre-drilling methods?

Petroleum geology hand in hand with geologists will always be in search of finding rocks on the surface, that for subsurface purposes these rocks are good oil storers, not only that but these rocks have good porosity which is the interconnected space where the oil will circulate, generating this in turn an excellent permeability (mobility of oil between pore spaces).

Geologists also try to detect geological structures called anticlines, this search for these structures is because they are structures where oil can accumulate, an example of an anticline on the surface is the following:

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As I have been explaining in the development of this article, petroleum geology is not limited to a possibility within their studies, analysis and evaluations, since for example in the case of anticline structures are not the only structures that serve as oil accumulating structures, for example geological structures such as faults and stratigraphic deposits serve to accumulate oil, the conclusion of the case is that the geology of oil before drilling is also behind the search for all this type of structure that represents a possibility to find the precious liquid.

Exploration while drilling

Once the petroleum geology, hand in hand with the geologists, has already identified the area that probably has hydrocarbons based on the exploration studies prior to drilling, then all these geological and petrophysical data are given to the engineers in charge of the drilling project, however not for this reason the geologists and petroleum geology will disappear in this important phase, remember that the drilling of the well is exploratory and it is where geological knowledge will be needed the most.

If we are going to analyze the geological techniques that are applied and used during the drilling of an exploratory well, we must say that these techniques are based primarily on collecting information about the lithological characteristics (porosity and permeability) of the formations that are crossed as the well is deepened, but this information is not obtained so easy, all this information is obtained through logs and tools that are lowered to the well.

To collect much of this geological information during the drilling of the exploratory well, two methods are used:

1. Direct methods:

They are called direct because you simply use a sample collects and obtain somewhat large cuttings of rocks, these cuttings are introduced inside the drill pipe while drilling, the important thing about collecting a sample of this type is that you can directly analyze the rocks and get an information of the petrophysical characteristics of the formation to which these rock cuttings belong.

1. Indirect methods:

Most probably we cannot obtain all the necessary information by direct methods, for this purpose indirect methods can be implemented, from which we can make a deeper description of the characteristics of the formations, especially those properties that we could not obtain from direct methods.

An exact test of applying an indirect method is to apply the technique of electrical logs, among which we have the spontaneous potential (SP), resistivity, radioactive logs (gamma ray, neutron and density), the important thing about the measurements of these logs as indirect methods is that they can provide us with the use of a correct reading quite convincing estimates about the quality of the rock and obtain the petrophysical properties such as porosity and fluid saturation (water, oil and gas).

Conclusions and contributions

For all those who have read this post have been able to realize that petroleum geology covers the exploration processes before and during the drilling of the exploratory well, generally the methods and techniques prior to drilling is an indication to select the area containing hydrocarbon.

However, it is not possible to affirm the existence of hydrocarbon in a given oil field until the well is drilled and starts producing oil, but all the previous information gathered before drilling is essential to give continuity to the geological studies that are carried out during drilling, such as the electrical logging runs in the well.

I hope this article has been able to cover many of the questions you may have regarding petroleum geology and the extent of this in the study and analysis in the search for hydrocarbons.

References

The geologist in the exploration and production of hydrocarbons

Geology in the search for petroleum. PDF Document