THE AIM OF THIS PROJECT IS TO IMPROVE THE KNOWLEDGE OF THE PHYSICAL PHENOMENA UNDERLAYING THE ENHANCED OIL RECOVERY AFTER A SECONDARY WATER INJECTION BY USING SURFACTANT SOLUTIONS.
Physical mechanisms involved when injecting an aqueous solution of surfactant are not very well known due to the poor knowledge of fluid mechanics in a porous medium and physicochemical mechanisms.
The research evaluated the effect of 2 physicochemical phenomena (coalescence and rigidity of the interphase between 2 fluids) on diphasic flows at low interfacial tension during tertiary recovery and the effect of interfacial tension reduction at the limits of a matrix block during spontaneous imbibition on oil recovery.
The study of the influence of coalescence, interface rhelogy, interfacial tension gradient on the diphasic flows in porous media induced the following conclusions:
the coalescence time of 2 droplets in an aqueous solution varied in accordance with the composition of the fluids in presence (this coalescence time can be evaluated outside the porous medium);
oil recovery was highly dependent on the coalescence time increasing as coalescence time decreased;
some fluid couples present very high surface viscosities (for the fluid couples tested, the interfacial shear viscosity increases as a function of time and was significantly non-Newtonian);
a high surface viscosity can significantly modify the pressure jump at the interface due to capillarity and this is all the more valuable as the pores are narrow and the flow itself is slow;
spontaneous imbibition can be correctly reproduced for 2 samples having similar petrophysical characteristics;
a decrease of the interfacial tension at the limits of a rock sample increases final oil recovery (the higher the desequilibrium between the aqueous and oil phases the better the oil recovery);
the oil recovery at the end of the imbibition, without lateral coating, is the same as the oil recovery at the end of imbibition with lateral coating (the imbibition kinetics were faster when imbibition was 3-dimensional than when was 1-dimensional);
a simulation model for imbibition, with interfacial tension gradient, w as developed (1-dimensional) and provided correct restitution of the experimental results, concerning the kinetics of the phenomenon.
IN A HOMOGENEOUS RESERVOIR, THE INJECTION OF A SURFACTANT AQUEOUS SOLUTION CAUSES PART OF THE DISCONTINUOUS OIL PHASE, LEFT BY A SECONDARY WATER INJECTION, TO MOVE. IN A FRACTURED-ROCK RESERVOIR THE ADDITION OF A SURFACTANT TO THE FRACTURE FILLING WATER SPEEDS UP THE KINETICS OF OIL RECOVERY BY SPONTANEOUS IMBIBITION. AS TO THE FIRST CASE, AT LEAST TWO CONDITIONS MUST BE SATISFIED TO ATTAIN A CONTINUOUS OIL PHASE: THE SURFACE TENSION GRADIENT ALONG THE POROUS MEDIUM MUST EXCEED A CRITICAL VALUE AND THE RATIO OF OIL/WATER VISCOSITIES MUST BE LOWER THAN A CERTAIN FUNCTION OF THE PERMEABILITY AND POROSITY OF THE MEDIUM. THE ROLE OF TWO FURTHER PARAMETERS WILL BE STUDIED: THE DROP COALESCENCE AND THE INTERFACIAL VISCOSITY. A METHOD WILL BE SET UP FOR COALESCENCE TIME MEASUREMENT EITHER BY A SIMPLE TEST-TUBE PROCEDURE OR BY A SPINNING DROP APPARATUS.
IN ORDER TO GET A RANGE OF COALESCENCE TIMES, AQUEOUS SOLUTIONS SHALL BE USED CONTAINING ABOUT 2% SURFACTANT (SULPHONATE), POSSIBLY SOME LOWER ALCOHOL AND SALT. THE SAME SOLUTIONS SHALL ALSO BE USED FOR EXPERIMENTS OF CONTINUOUS BIPHASIC FLOW AS WELL AS OF RESIDUAL OIL DISPLACEMENT IN POROUS SYSTEMS. THE OBSERVED BEHAVIOUR WILL BE RELATED TO THE COALESCENCE TIMES.
CRUDE OIL IN THE PRESENCE OF SURFACTANTS SHOWS CONSIDERABLE INTERFACIAL VISCOSITY WITH RESPECT TO WATER. THE AIM IS TO DEVELOP SOME FLUID COUPLES WHICH WILL ALLOW THE EFFECT OF THIS PARAMETER TO BE EXAMINED BOTH BY CAPILLARY FLOW AND BY EXPERIMENTS IN POROUS MEDIA ANALOGOUS TO THE PREVIOUSLY MENTIONED ONES. ADDITIVES LIKE BSA OR SDS WILL BE USED: THE OIL PHASE WILL CONSIST OF A MIXTURE OF OCTANE AND "ALBELF" (VISCOSITY - 1CPO, 0.7AS TO THE FRACTURED RESERVOIR CASE, THE OBJECTIVE IS TO QUANTITATIVELY EVALUATE THE SURFACTANT ADDITION EFFECT ON THE KINETICS OF SPONTANEOUS IMBIBITION. TWO SAMPLES OF STRONGLY HYDROPHILIC POROUS MATERIALS WILL BE PROPERLY CONDITIONED AND DIPPED INTO THE AQUEOUS PHASE CONTAINING THE SURFACTANT AT ROOM TEMPERATURE AND PRESSURE AND THE OIL RECOVERY CONTINOUSLY RECORDED AS A FUNCTION OF TIME. FLUID COUPLES WILL BE SELECTED SO AS TO GET AT LEAST FOUR DIFFERENT INTERFACIAL TENSIONS BY KEEPING THE VISCOSITY RATIO AND DENSITY DIFFERENCE CONSTANT.