Gerardo Clemente Martinez
Mexican Association of Exploration Geophysicists
Expert Contributor

Exploration: How it Works, From a Geophysicist’s Perspective

By Gerardo Clemente | Thu, 05/12/2022 - 18:00

Often when we talk about the oil industry, the first thing that comes to mind is a refinery or production facility, or a drilling platform or oil well. We also talk about the price per barrel, the amount of reserves and daily production. However, little or almost nothing is said about all the activity that is carried out to locate where an oil well should be drilled. Oil exploration is an activity of which little is mentioned but which denotes a great deal of knowledge that evolves daily and where considerable use of technology is made and with a relatively low investment, compared to the resources that production and the refining of hydrocarbons entails.

The exploration triggers the entire hydrocarbon industry.

Exploration is a learning process that evolves as we better understand what we are looking for. In the beginning, we searched formations that were similar to those of the fields that were already producing. Later, it was understood that hydrocarbons are accumulated in porous and permeable rocks, which should be encased in impermeable rocks that would allow hydrocarbon entrapment. This led us to the concept of the petroleum system, which consists of five elements: the presence and quality (porosity and permeability) of reservoir rock; the presence and impermeability of the seal rock; the source rock, with an abundance of organic matter trapped in anoxic conditions and at a depth that allows pressure and temperature conditions for the generation of hydrocarbons (maturity); the trap, with a geometry and arrangement of the reservoir rock and seal rock that allow the accumulation of hydrocarbons; and the synchronization and migration pathway, which consists of the hydrocarbon being expelled from the source rock and migrating in search of areas of lower pressure after the trap has been formed, causing its entrapment.

Later still came the understanding of the relationship between the source rock and the reservoir rock within several prospects in the same basin, giving rise to the concept of Play (Magoon and Dow, 1994) and with this, consolidating the method of evaluating the basins of the world, ranging from the regional studies of thousands of square kilometers to the particular prospects tens of square kilometers, and through the play scale of hundreds of square kilometers.

Once it is understood what we are looking for, we establish a strategy to accumulate knowledge of the basins with each exploration and production well that is drilled. This strategy has been called the exploration process, which I, in particular, would call the exploration cycle because we began with the recognition of large areas, reconstructing the geological history, postulating with the information available the paleoenvironments of deposit and the deformation they suffer through the tectonic evolution of the crust. We identify the elements of the petroleum system, with a very important task in each stage, which is the risk assessment. We call this first stage potential evaluation, where at the regional level we prove the existence of source rock. The presence of reservoir rock and seal rock is identified and evidence of hydrocarbon generation is sought.

Subsequently, once the relationships between source rock(s) and reservoir rock(s) are linked, generating hypothetical plays, documenting prospects and the risk assessment of the presence of each of the elements of the petroleum system, defining the volume of potential resource to be incorporated versus the risk that exists, as well as the cost-benefit ratio, which will be a ranking criteria. This determines which prospects will be drilled first.

When a prospect is drilled and becomes a commercial producer, a proven play is established and this is the second stage, called reserves incorporation. With the information acquired from the well, the regional model is updated. We then evaluate the discovery and transfer the field development team, which is the third and final step of the exploration cycle. Each time, a well is drilled or new information is acquired and, based on this, along with the success ratio, the oil price and geopolitics, we delineate the exploration strategy.

This is a rough summary of the tasks performed by geologists, geophysicists and geoscience engineers, supported by biostratigraphers, geomaticians, information technology specialists and a large number of specialists who help locate favorable areas for hydrocarbons accumulations. Through the generation of evolutionary models of the Earth's crust, the use of principles and laws and supported by the acquisition of indirect information (geophysical information) calibrated with information from wells, and through the use of state-of-the-art computational algorithms, as the basin matures, the better understanding we have of it.

From my perspective, the exploration of subsoil energy resources is a way of life where we manage space and time over the planet’s 4.5 billion years of geological evolutionary history.