MAIN PURPOSE OF THE PROJECT IS TO INVESTIGATE TROUGH LAB EXPERIMENTS,AND TO PREDICT WITH NUMERICAL MODELS THE COMPLEX PHENOMENA OF SCALE DEPOSITION OCCURING IN OIL RESERVOIRS WHERE IT IS INJECTED WATER NOT COMPATIBLE WITH THE FORMATION BRINE.
Laboratory experiments were carried out to measure the solubility of calcium sulphate and barium sulphate dissolved in natural aqueous systems.
The EQ3NR/EQ6 chemical model was successfully used to simulate the experiments on barium sulphate precipitation but used too much central processing unit (CPV) time. Specific programs able to process each scaling salt were developed (assuming the actual solutions could be replaced by equivalent systems) and the chemical equilibria of these systems were characterized by matrix of data or empirical relationships. The validity of the models was checked by matching the results of solubility experiments.
The porosity and permeability reduction caused by salt precipitation in a porous medium was measured. The results showed that the scale formation can seriously impair the rock permeability, mainly for the sandstones. For limestones and dolomites part of the rock was removed by the injected waters. The scale formation mechanism was studied involving oil saturating sandstones of different wettability. It resulted that the plugging of pores did not affect the oil recovery process or the values of residual oil saturation.
A numerical model able to simulate the injection of incompatible waters in aquifers was developed. A pseudocell was used to describe the scale formation at producer wells.
Cases were run simulating the barite precipitation in a 5-spot injection pattern. From the results it appears evident that 3 fronts (mixing, scaling, temperature) travel through the aquifer at very different velocities.
The model runs showed that the scale deposition caused a very small porosity reduction at the injection well and in the aquifer body. On the contrary the amount of solids precipitated at the pseudocell was very high and increased rapidly with the time causing a severe permeability reduction.
THE PROJECT IS TO BE DEVELOPED IN THREE MAIN PHASES:
PHASE 1 - SCALE EXPERIMENTS BY MIXING NOT COMPATIBLE WATERS AT DIFFERENT TEMPERATURE. DEVELOPMEMNT AND TESTING OF SIMPLIFIED MODELS ABLE TO PREDICT THE CHEMICAL EQUILIBRIUM OF AQUEOUS SOLUTIONS. MEASUREMENTS OF ABSOLUTE PERMEABILITY REDUCTION DUE TO SOLIDS PRECIPITATION IN ROCKS OF DIFFERENT LITHOLOGIES.
PHASE 2 - LAB EXPERIMENTS OF SCALE DEPOSITION BOTH IN WATER-WET AND OIL-WET ROCK SAMPLES. DEVELOPMENT AND TESTING OF A 2-D NUMERICAL MODEL ABLE TO PREDICT THE PRESSURE/TEMPERATURE DISTRIBUTION AND THE SCALE FORMATION IN CASE OF INJECTION OF NOT COMPATIBLE WATER IN AN AQUIFER.
PHASE 3 - EXTENSION OF THE MODEL, BUILT IN PHASE 2, TO THE CASE OF AN OIL BEARING FORMATION.