Structural and Mechanical Characteristics of Molecular-Surface Interaction in the Reservoir System "Oil - Chemical Solution - Porous Medium" During Waterflooding
Authors: Kotenev M. , Robertson Fugro , Kondrashev O. , Kotenev Y. 
Published: June 2014

Physics of surface effects in porous medium in relation to structural-mechanical mudding was investigated. The micro-rheology of surfactants effect on reservoir fluids was studied. Scientific basis for enhanced oil recovery techniques application was developed.

Low efficiency of low-concentrated solutions of non-ionic surfactants during flooding is linked to a number of factors that reduce relatively high laboratory evaluations of cleaning and displacing characteristics of individual surfactants - low surface activity of agent on border with oil, significant reduction of surfactant contents on displacement front due to high adsorption losses and shaft of buried water.

Filtration and micro-rheology research, conducted on original installation which allows to explore structural and mechanical properties of reservoir fluids in pores of µm size, showed that crucial role is played by another factor - the twofold effect of surfactants on film oil. This effect, previously noted in high-molecular systems, was defined by us for the low-molecular components of reservoir system "oil - surfactant solution - porous medium". The phenomenon essence lies in the surface and volumetric mechanisms of surfactants influence on the film oil. Firstly, there is a well-studied adsorption on active centres of solid body, what reduces structuring effect of the solid field on near-wall layers of liquid. Volumetric mechanism is due to diffusion of surfactant in liquid and reduction of cohesive interactions in liquid. Their combination can lead to both weakening and strengthening of non-Newtonian and filtration anomalies of film oil.

Proven that even light asphalt-resinous oil in pores with diameter of 1 – 4 µms acquires properties of solid rheological body, which depend on ratio of intensity of intermolecular interactions within the fluid and at its external borders. Introduction of surfactant, changing balance of these forces leads to increase or decrease in rheological and filtration anomalies of film oil. Mixed effects of surfactants on residual oil, complexity of maintenance of optimal reagent concentration at displacement front does explain results of field tests of this method, which requires additional non-standard laboratory tests and strict compliance of application technology in the field.

Direct measurements of structural-mechanical and hydrodynamic liquid parameters in tight gaps – flat capillaries in reservoir conditions have been carried out. The extreme character of concentration dependencies of hydrodynamic properties of capillary oil proves the possibility of oil effect mechanism change by variation of reagent concentration in the displacing fluid. The study defined more precisely physical-chemical peculiarities of membranous oil condition – impact of intensification methods and estimate its effectiveness degree. New methodology of studies included analysis of structure forming kinetics and the specifics of oil from three oil fields before and after reagent contacts in tight gaps, which correspond for average pore dimensions of low-, medium- and high-permeable reservoirs under development. Study has been carried out with reagents of different character. Proposed reagents meet major criteria for flow deflection technologies, helping on the first stage washing of oil in washed parts of reservoir and decreasing its permeability, subsequently. Extensive research allowed developing appropriate enhanced oil recovery technologies and it successful realization in the field.