Results of oil displacement laboratory tests during field simulation, using various inhibitors

Various simulation methods are required for accurate evaluation of oil recovery enhancement efficiency. One of them is physical simulation, performed in core samples of reservoirs and commonly defining as one of the key displacement parameters. The results of laboratory tests, concerning with defining displacement index of formation stimulation, using various inhibitors (core models of particular development targets): nitrogen, carbon dioxide, separated gas and cyclic water-gas stimulation, are provided in the article.
Materials and methods
The filtration experiments were carried out, using special two-phase laboratory unit, manufactured on the basis of the system for defining relative phase permeability. Rock permeability, according to Klinkenberg allowance, as per GOST 26450.2-85, was measured in dry core samples.The residual water saturation was created in the core samples with the methodsof centrifuging and semi-permeablemembrane. The filtration experiments were carried out, using core samples under the conditions of simulating productive reservoirs of the fields. Simulation of formation conditions was carried out under the temperature conditions, fully corresponding to the real reservoir conditions, and the pressure conditions were simulated, according to the efficient pressure.
Results
According to the results of light oil displacement by various inhibitors in the core of the Urengoyskoe and Zapolyarnoe fields, the most effective technologies are: the injection of gas and water and carbon dioxide miscible displacement. Gas-oil displacement by nitrogen and separated gas proved to be of less efficiency.
Сonclusions
Laboratory tests helped to know more about the fluid filtration of the Lower Cretaceous deposits of the Urengoy and Zapolyarnoye fields under the influence of gas and water-gas injection. Finally, it was stated that highefficiency of water-gas injection is caused by less fluidity, considerably reducing the filtration velocity of the displacing inhibitor, the filtration pressure gradient is growing and, thus, oil displacement is increasing. High efficiency of oil displacement by carbon dioxide in comparison with nitrogen and separated gas is determined by its high solubility in oil. When the level of oil saturation by carbon dioxide is highest, volume of dissolved gas will be significantly higher than volume of methane, dissolved in the same oil under the same temperature and pressure conditions. Less efficiency of oil displacement by methane and nitrogen is caused by worse solubility in oil and negative oil-gas viscosity ratio (above 30). Though methane has better solubility in oil than nitrogen, R&D results of oildisplacement are almost the same. This is due to the fact that oil of under-gas-cap-zone is not dissolved by methane and nitrogen.