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Discover the steps and technologies used to find and evaluate reserves of onshore oil, from initial geological studies to drilling and declaration of commerciality.
The search for onshore oil is a complex and scientific undertaking. It involves advanced technology, high risk and significant investment. Far from being haphazard, exploration follows a rigorous, phased process. This guide details how onshore oil is found.
Surface geology and geochemistry
Onshore oil exploration starts with identification of promising sedimentary basins. Geoscientists map rocks on the surface. They analyze aerial photographs and satellite images. They also look for seeps of oil or gas.
Studies of stratigraphy (rock layers) and structural geology (faults, folds) help to understand the underground architecture. Geochemical prospecting complements this phase. It analyzes gases in the soil or the presence of specific microorganisms. These techniques look for chemical anomalies that may indicate the presence of hydrocarbons at depth.
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Geophysical investigation: the “eyes” beneath the earth
After surface studies, geophysical investigation “visualizes” the subsoil. The goal is to map geological structures and identify potential onshore oil traps.
Seismic surveys (2D and 3D) are the main tool. Acoustic waves are generated at the surface. Their reflections from the rock layers are recorded by geophones. This processed data creates images of the subsurface.
Other methods include gravimetry, which measures variations in the gravitational field. Magnetometry measures variations in the magnetic field. Both help delineate basins and deep structures. Geoelectric methods measure the resistivity of rocks, indicating fluid types. Integrating all of these geophysical and geological data builds an exploratory model.
Exploratory drilling
Once a promising location (prospect) has been identified, an exploratory well is drilled. This pioneering well, called a “wildcat,” is the moment of truth. It tests geological hypotheses and confirms or denies the presence of onshore oil.
Onshore drilling rigs perform the operation. They use steel tube columns, special drill bits and drilling fluids (mud). As the well advances, it is lined with steel and cemented to ensure stability and safety. Technologies such as directional and horizontal drilling are used to optimize access to the reservoirs.
Confirming the discovery of onshore oil
After reaching the target depth, the well is evaluated. Well logging uses probes with sensors. These sensors measure physical properties of the rocks, such as resistivity and radioactivity. They help identify the type of rock and the fluids present.
Formation Testing (DST) is performed to assess the productive capacity of a zone. It measures the flow and pressure of fluids and collects samples. Analysis of cores (cylindrical rock samples) provides detailed data on porosity, permeability and fluid saturation.
From discovery to commerciality
The mere presence of oil onshore does not guarantee its extraction. The discovery must be commercially viable. The operating company notifies the regulatory agency (such as the ANP in Brazil).
A Discovery Evaluation Plan (DEP) may be required. This plan includes drilling of additional (appraisal) wells and additional seismic. A detailed technical-economic analysis is performed. It considers recoverable volumes, development and operating costs, and the price of oil.
If the analysis is positive, the company declares the commerciality of the discovery. It then presents a Development Plan for the production of the onshore oil field.
Brazilian onshore oil scenario
Onshore oil exploration benefits from constant innovation. Artificial Intelligence (AI) and Machine Learning are used to analyze large volumes of geoscientific data. This aids in seismic interpretation and reservoir modeling.
Advances in seismic acquisition, drilling and logging technologies increase efficiency and accuracy. In Brazil, onshore basins such as Recôncavo, Potiguar, Solimões and Parnaíba remain relevant. The National Agency of Petroleum, Natural Gas and Biofuels (ANP) and the Geological Survey of Brazil (SGB/CPRM) act to foster and regulate the onshore oil sector.
