Petroleum Industries frequently deal with environmental problems which have their origins in accidental spills during operations of exploration, transport, refining and storage of oil and of its derivates. After being spilt on the ground, oil products infiltrate into the soil in a smaller or greater scale according to the porosity and moisture content of the ground and the chemical and physical proprieties of the spilt products. Because of its non-polar nature, solubility in water of petroleum products is very small; therefore, a dissolved fraction and an undissolved fraction will co-exist in the sub superficial medium. This latter fraction constitutes a Non Aqueous Phase Liquid or NAPL. The NAPL is composed almost exclusively by hydrocarbons and moves in the subsoil independently of the dissolved fraction (aqueous). NAPL products can have a greater density than water, forming a Dense Non Aqueous Phase Liquid (DNAPL), or they can have a ; smaller density than water, forming a Light Non Aqueous Phase Liquid or LNAPL. Most LNAPL ii contamination problems are probably originated by spills of petroleum derivates such as gasoline, diesel and fuel oil.
When a great amount of LNAPL is spilt on the soil, it will gradually move downwards until, eventually, it will reach the water table, forming a groundwater contamination source. Reaching the water table, LNAPL forms a film that floats freely on its surface and whose motion is controlled by the hydraulic gradient and by the pressure distribution on the LNAPL film.
Nowadays there are numerous technologies and processes (some more developed than others), that are designed to recover aquifers contaminated by LNAPL products. However, whenever there is an LNAPL film on an aquifer surface, the first measure to take is to remove the free fraction of LNAPL as far as possible; thus, in this stage, the first task is to attack the problem by extracting the non-aqueous phase with a pump. Therefore, the number of wells, the distance between them and their flow (only for LNAPL or for water and LNAPL) constitute some of the decision variables in the recovery project for LNAPL contaminated aquifers.
In this thesis, which has its origin in the participation of the Departamento de Minas da Faculdade de Engenharia da Universidade do Porto in environmental studies concerning the Refinaria do Porto da Petrogal, an attempt has been made to define the way in which some of those variables are related with the light hydrocarbon film movement and the way they condition the film thickness at the end of pump cleaning operations.
In this context, a set of equations has been developed for the saturated bi-phase flux system, for water and a light non-aqueous liquid in the stationary case. The solutions to these equations were implemented by analytical and numerical methods through algorithms of automatic calculus. The explorations of these algorithms has allowed the validation of the obtained results and define its potentialities. Additionally, a laboratory model was built to physically simulate the problem of a well in the middle of an island in an LNAPL contaminated sea. The parameters related with the fluids movement in that model were experimentally determined and the results obtained in the model were compared with the results given by the algorithms of automatic calculus. Finally, and with the objective of applying some of the established conclusions to the actual problem present in Refinaria da Petrogal, a statistical correlation study was done between the piezometric data and the monthly precipitation. This study has permitted the construction of a statistical model to predict the piezometric level of water as a function of the rainfall and to estimate the extreme positions of the water table in the refinery terrains. The results of that model were then input into a groundwater flux numerical model, thus allowing the simulation of different scenarios of escape and capture of the light petroleum products that are underneath the refinery lands.