# An Unsupervised Anomaly Detection Based on Self-Organizing Map for the Oil and Gas Sector
## 3 The Research Approach
### The Experimental Two-Phase Plant  
The gas-liquid biphasic system is characterized by the presence of two phases, a gaseous and a liquid one, in thermodynamic equilibrium. Although the gas and liquid are intimately mixed, they maintain their distinct physical properties, such as density, viscosity, and surface tension.  
The two-phase experimental plant is located at the Department of Industrial Engineering and Mathematical Sciences (DIISM) of the Universita Politecnica delle Marche (Ancona, Italy). The 3D plant model is shown in Figure 3, and some views of the actual plant are in Figure 4. It reproduces the extraction of oil and natural gas from depleted wells. Specifically, the useful life of hydrocarbon reservoirs is related to their potential and operating costs. A well is depleted if the water in it is in such quantities that it cannot be extracted or if the volumes of hydrocarbons produced become uneconomic considering the very high operating costs to make them unsustainable if there is little or no production. In such circumstances, the most obvious solution would be installing appropriate pumps located on the surface and at the base of the oil well with a very high cost compared to the produced hydrocarbon volumes. The system under consideration represents an undoubtedly more efficient solution. The extraction from a depleted reservoir is carried out by using the pressure of a hypothetical reservoir at the height of its useful life. Due to its physical characteristics, the latter's pressure is higher than the transport pressure and, therefore, is able to create suction on the depleted reservoir, which, in contrast, does not have enough pressure for transport on the line.  
Gas-liquid ejectors can mix two phases at different pressures (depletion and good wells) and impart the necessary transport energy. While in a realistic situation, the fluids treated are crude oil and natural gas, for safety reasons, water and ambient air are used in the case of the experimental plant. Specifically, water in a tank and a positive displacement pump model pressurized well behaviour, while ambient air simulates natural gas from a depleted reservoir. Pressurized water (\"INLET WATER\") enters the ejector, creating a vacuum that draws in a certain amount of air from the environment (\"INLET AIR\"), thus creating a two-phase mixture (\"INLET MIXTURE\"). The resulting mixture is directed into a vertical tank that acts as a slug catcher to separate the liquid (\"OUTLET WATER\") and gas (\"OUTLET AIR\") phases. The plant is equipped with three pneumatic valves: to control the inlet water pressure (V1), regulate the pressure inside the tank (V2), and regulate the water level (V3). All the \"VMs\" in Figure 3 represent shut-off valves used to reproduce anomalies in the system.  
Table 2 briefly describes the plant equipment characteristics in terms of the monitored variable, the unit of measurement, type of equipment, and finally, the equipment tag code. All the plant sensors and valves are connected to a Revolution Pi device to acquire their status value.