Rock samples reveal the Earth’s history.
Rock samples reveal the Earth’s history.
The first rock samples were sent to Eni in the 1930s, in the early days of oil exploration. Today, those samples – and all others drilled over the years – are a treasury of information. Core samples provide a vertical cross-section – and therefore a historical record – of our reserves of hydrocarbons. They tell us the age of the rocks, measure their porosity and permeability and enable us to plan our production of hydrocarbons over time. They also help us to understand the environment in which they are deposited. Analyses of rocks and fluids performed in our laboratories are an essential part of our Upstream business. Our laboratories – equipped with cutting-edge instruments such as X-ray tomography machines that can visualise the movements of fluids in core samples ─ provide technological solutions to the problems faced by our technical units.
Once in the laboratory, the core samples are examined by our technicians. Analysis enables us to reconstruct what has happened over millions of years inside the oilfield we are investigating. This is how we do it:
Andrea Ortenzi, chief technician at our Bolgiano facility, is our guide for a tour of the Geology Laboratory, point of entry of all the samples of rocks and fluids taken from our oil wells around the world. “To read the history of an oilfield by studying samples, we first have to find the oilfield,” he says. But how do you discover an oilfield? Know-how, innovation and teamwork provide the foundations of our success – starting with the technology needed to explore the Earth in depth.
Andrea Ortenzi, Eni geologist
In this video interview, Luca Visconti, speaking from our Oil Engineering Laboratory, explains the petro-physical characteristics of the rock samples. Using an X-ray micro-tomograph, we acquire 3D images of the internal structure of the core sample at a resolution of up to 1 micron/pixel.
Passion and patience are the trademarks of the petrographer, whose job is to study the history and quality of rocks and determine their efficiency index. At least 50 per cent of hydrocarbons are contained in the pores of sedimentary rocks that comprise fragments of other rocks – type known as “terrigenous”. The quality of a reservoir depends on its original characteristics and the evolution of its internal structure ─ variables studied by the geological discipline of petrography. With passion and patience, the petrographer measures all the critical variables: the size of the rock grains, the type of components present when they were deposited and those that have been generated over time. He also measures the size and spatial arrangement of the “negative” of the solid rock – its pores, which contain the hydrocarbons. The rock’s diagenesis (the physical and chemical changes associated with the dissolution of the original grains and the precipitation of new minerals in the pores after the original sand has been deposited), linked with the thermal history of the rock, determines the quality of the reservoir. By observing the geometrical relationships between the various minerals that have formed in the pores, and conducting analyses to determine the temperature at which these processes occurred, it is possible to reconstruct the sequence of these events – their so-called diagenetic history. We now have all the ingredients of the recipe – and that enables us to predict the quality of our oilfield before any wells have been drilled. The quantitative and qualitative information gathered in this way is condensed into an index that expresses the quality of the rock itself. This reservoir efficiency index (e-rei) reflects the reservoir’s permeability and porosity and is sensitive to every variation of its diagenesis, dependent on changes in thermal history and sedimentation. The e-rei values will be used by explorers and by those whose task it is to construct models to optimise the development and production of the oilfield.
Each type of rock is characterised by certain values of density, which can be reconstructed. Thanks to Gravity Gradiometry (GG) technology, we can obtain valuable information on the type of rocks in the area and on their geometries in the subsoil. Eni has been a pioneer in the use of this type of data since the turn of the millenium.