THE AIM OF THIS PROJECT IS THE DIRECT THERMODYNAMIC AND STRUCTURAL CHARACTERIZATION OF THE ORGANIZED INTERFACIAL AREAS OF SURFACTANT MICROEMULSIONS USED IN TERTIARY OIL RECOVERY, THUS ALLOWING IMPROVED SIMULATIONS OF THEIR BEHAVIOUR DURING THEIR TRAVEL THROUGH POROUS MEDIA.
The research investigated the 2-dimensional domains which occur between the oil and the water when water, oil, surfactant and alcohol (or any cosurfactant) are mixed.
The phase diagram of the ternary hexanol, heavy water, sodium dodecyl sulphate (SDS) system was determined. Then a systematic study of the deuterium nuclear magnetic resonance (NMR) signal of the heavy water was performed for the different compositions corresponding to the lamellar domain encountered. It was shown that all the variations observed within the whole set of data obtained could be explained in terms of a very simple hydratation process: the SDS molecules were completely hydrated by 8 water molecules while 5 (or 6) are sufficient for the alcohol ones.
As the hydroxylic radical of the hexanol had been exchanged with the appropriate part of a number of heavy water molecules, the opportunity arose to examine the corresponding signal of NMR. After having computed the contribution due to the exchange process, a theoretical description accounting for the variations of the quadrupolar splittings observed was proposed. THis was made in term of a complexation equilibrium between the 2 kinds of molecules present in the bilayer. The relevant thermodynamical constant could not be defined from these experiments.
In order to try to determine this equilibrium constant, an alpha deuterated molecule of alcohol was synthesized and the same experiments as above were realized with this new molecule. The results could be explained by the precedingly introduced complexation equilibrium and the numerical value of the constant characterizing the assumed equilibrium (k=3) was found.
To check the validity of the hypothesis and alpha deuterared molecule of SDS was synthesized and the same series of experiments were performed it appeared that the experimental results could not be accounted by the equilibrium law previously considered. The whole set of results (alcohol and SDS) has then been considered withi n the frame of a fluctuation theory. This theoretical approach, led to the determination of the bending modulus kc.
WHEN A SURFACTANT-COSURFACTANT AQUEOUS EMULSION IS INJECTED IN A WELL FOR TERTIARY OIL RECOVERY, A RAPID LOSS OF EFFICIENCY OCCURS AS A RESULT OF THE EXCHANGES THE COMPONENTS UNDERGO WITH THE OIL AND WATER PHASES DURING THEIR TRAVEL THROUGH THE POROUS MEDIUM. MODELLING OF THE COMBINED PROCESS OF EXCHANGE AND FLOW HAS BEEN UNDERTAKEN BY AUSTIN UNIVERSITY (PROF. POPE) AND SUBSEQUENTLY MODIFIED BY INTRODUCING THE "PSEUDOPHASES" CONCEPT DEVELOPED BY THE PHYSICAL CHEMISTRY DEPT. OF BORDEAU UNIVERSITY.
IMPROVED SIMULATIONS HAVE ALREADY RESULTED SINCE THE INTRODUCTION OF SUCH A CONCEPT. A BETTER APPROACH TO THE STUDY OF THE STABILITY OF SUCH SYSTEMS, UNDER STUDY BY IFP, WILL ALSO RESULT. ACCORDING TO THIS VIEW THE SYSTEM WATER (W)/OIL (O)/SURFACTANT (S)/COSURFACTANT (C) CAN BE REPRESENTED BY THREE COEXISTING PSEUDOPHASES, ONE OUT OF THE THREE BEING THE MEMBRANE -SHOWN TO BE STRUCTURALLY ORIENTED - SEPARATING THE FIRST TWO. THE PURPOSE OF THE RESEARCH WORK IS TO DIRECTLY DETERMINE THE PARTITION CONSTANTS CONCERNING THE MEMBRANE PSEUDOPHASE.
MICROEMULSIONS CONSISTING OF WATER (W), DODECANE (O), NA DODECYLSULPHATE (S) AND HEXANOL (C) WILL BE INVESTIGATED IN TWO STAGES. THE FIRST ONE WILL BE CONCERNED WITH THE CHARACTERIZATION OF THE PHASE DIAGRAM OF THE SYSTEM WSC THUS ALLOWING THE PHYSICO-CHEMICAL STUDY OF THE ORGANIZED PHASES THERE ENCOUNTERED TO BE EFFECTED. A HIGH RESOLUTION NMR SPECTROMETER SUITABLE FOR SOLUBLE STATE INVESTIGATIONS AS WELL AS A LIGHT SCATTERING APARATUS EQUIPPED WITH A VERY FAST DATA ACQUISITION SYSTEM, PURCHASED IN THE MEANTIME, WILL PERMIT THE SECOND STEP TO BE UNDERTAKEN.
THIS IS AIMED AT THE CHARACTERIZATION OF THE PSEUDO-CONSTITUENTS OF SUCH ORGANIZED PHASES (BY NMR). THE ASCERTAINMENT OF THEIR PSEUDO-CONSTITUENTS NATURE OVER THE WHOLE AREA OF VALIDITY OF THE PSEUDOPHASE MODEL WILL BE PERFORMED BY A LIGHT SCATTERING STUDY. THIS WILL PROBABLY PERMIT CONCLUSIONS TO BE DRAWN AS TO THE HYPOTHESIS THAT THE ORGANIZED PHASES WILL BE SWOLLEN BY EITHER OF THE PSEUDOPHASES (WATER OR OIL) IN EQUILIBRIUM WITH THEM.
THE WHOLE OF THE EXPERIMENTAL RESULTS WILL ALLOW THE CALCULATION OF THERMODYNAMIC PARTITION CONSTANTS OF THE SYSTEM TO BE CALCULATED. THE EXPLOITATION OF THE MODELS THUS IMPROVED WILL BE MADE IN CLOSE COOPERATION WITH S.N. ELF AQUITAINE.