THE MAIN OBJECTIVE OF THIS PROJECT IS TO ELABORATE FUNDAMENTAL KNOWLEDGE ON THE INTERACTIONS BETWEEN THE HIGH MOLECULAR WEIGHT WATER SOLUBLE POLYMERS CURRENTLY USED IN ENHANCED OIL RECOVERY OPERATIONS (EOR) SUCH AS POLYACRYLAMIDES AND THEIR DERIVATIVES AND XANTHANS,AND THE MINERAL SURFACES FREQUENTLY FOUND IN NATURAL RESERVOIR ROCKS.
INDEED, THE LACK OF KNOWLEDGE ON POLYMER-ROCK INTERACTIONS IS THE MAIN OBSTACLE FOR REDUCING THE RISKS OF FAILURE IN POLYMER FLOODING AND FOR OPTIMIZING THIS PROCESS BY IMPROVING ITS ECONOMICAL VIABILITY.
FOUR MAIN GOALS WERE DEFINED FOR THIS PROJECT:
1) ACQUISITION OF SCIENTIFIC BASIS FOR SELECTING THE BEST POLYMER FOR A GIVEN APPLICATION
2) DEFINITION OF A METHODOLOGY FOR OBTAINING RELIABLE EVALUATION OF POLYMER LOSSES BY ADSORPTION AND RETENTION IN A GIVEN RESERVOIR
3) MINIMALIZATION OF THE RISKS OF MECHANICAL DEGRADATION
4) DETERMINATION OF THE BEST CHEMICAL STRUCTURES FOR EOR POLYMERS.
The low efficiency of water flooding for producing oil from reservoirs is greatly improved by the addition of water soluble polymers to injection water, decreasing water mobility and thus improving reservoir sweep efficiency. The mechanisms involved in this technique, known as polymer flooding, were analysed.
Electron spectroscopy for chemical analysis (ESCA) was a very efficient technique for determining the nature of surface groups and for measuring, under given salinity conditions, the amounts of ions adsorbed on the mineral surfaces. The adsorption of xanthan and polyacrylamides onto kaolinites and siliceous minerals was strongly influenced by the presence of calcium.
The adsorption of polymers was dependent on the nature of monovalent cations in the solution; as cation hydration decreases, adsorption increases. This phenomenon arose from the fixation of ions on both the polymer and the surface which is governed by a competition between electrostatic and hydration forces. For all cations, adsorption increased with salinity. The additon of anions such as sulphites or phosphates in the injection water can produce a strong decrease in polymer adsorption of siliceous minerals and kaolinites. However, the adsorption on montmorillonite was not affected by the presence of anions. Phosphates were more efficient than sulphites. The effects of oxygenated anions on polymer adsorption were attributed to their fixation of ligand exchanges on the hydroxyl groups of mineral surfaces, reducing attractive forces between polylera and surface.
The role of salinity and shear rate on polymer mechanical degradation during flow through porous media has been investigated and quantified. An original result showing the very important influence of oxygen which can accelerate polymer degradation has been obtained.
The introduction of sulphonated groups into a polyacrylamide chain has been shown to lead to a decrease in adsorption densities on siliceous minerals and on kaolinite. Rh eological properties have been investigated; stationary, complex dynamic and elongational measurements have been performed.
DUE TO THE HIGH COMPLEXITY OF THE PHENOMENA, THE FIRST PART OF THE WORK WILL BE FOCUSED ON THE STUDY OF MODEL SYSTEMS MADE OF PURIFIED AND WELL-CHARACTERIZED POLYMERS AND MINERAL SURFACES. IN A SECOND PART, THE BEHAVIOUR OF POLYMERS IN MORE COMPLEX NATURAL MEDIA WILL BE STUDIED.
THE PROJECT HAS BEEN DIVIDED INTO FOUR DIFFERENT PHASES:
PHASE 1: SYSTEM CHARACTERIZATION
POLYMER SOLUTIONS: DETERMINATION OF CHEMICAL STRUCTURE (HYDROLYSIS DEGREE FOR POLYACRYLAMIDES, PYRUVATE AND ACETATE CONTENT FOR XANTHANS) AND MOLECULAR WEIGHT, CHARACTERIZATION OF POLYMER IN SOLUTION: INTRINSIC VISCOSITY, HUGGINS CONSTANT, RADIUS OF GYRATION AS A FUNCTION OF PH AND SALINITY, RHEOLOGICAL CHARACTERIZATION IN SHEAR FLOWS.
MINERALS: METHODS OF SURFACE PREPARATION, DETERMINATION OF SURFACE SITES AND ION ADSORPTION BY ESCA, SPECIFIC SURFACE, SURFACE CHARGE USING POTENTIOMETRY, ELECTROKINETIC POTENTIAL. X RAYS AND ELECTRONIC MICROSCOPY FOR NATURAL ROCK CHARACTERIZATION.
PHASE 2: ADSORPTION ON POWDERED MINERALS
METHODOLOGY FOR OBTAINED RELIABLE AND ACCURATE MEASURMENTS. EFFECTS OF SOLID TO LIQUID RATIO DUE TO SELF-AGGREGATION OR FLOCCULATION. INFLUENCE OF MAIN PARAMETERS GOVERNING ADSORPTION PROCESS: PH, SALINITY INCLUDING MIXTURES OF DIFFERENT IONS, TEMPERATURE AND POLYMER IONISITY.
ADSORPTION ON DIFFERENT TYPES OF MINERAL SURFACES, FREQUENTLY FOUND IN RESERVOIR ROCKS: SAND, CLAYS AND CARBONATES. CLAYS EXHIBIT SURFACES HAVING DIFFERENT MINERALOGICAL AND CHEMICAL STRUCTURES WHICH ARE MORE OR LESS ACCESSIBLE TO POLYMER MOLECULES DEPENDING ON ROCK STRUCTURE. THE ADSORPTION LEVELS WILL BE DETERMINED ON BASAL AND LATERAL SURFACES OF KAOLINITES (SILICATE, ALUMINIUM HYDROXYDE AND SILICO ALUMINATE), MONTMORRILLONITE, ILLITE, GIBBSITE AND CHLORITE. THE MAIN MECHANISMS OF ADSORPTION (VAN DER WAALS, HYDROGEN BONDING, ELECTROSTATIC, ENTROPY) WILL BE DETERMINED IN ORDER TO FIND OUT THE POSSIBILITY OF REDUCING ADSORPTION LEVELS.
PHASE 3: RETENTION IN POROUS MEDIA FLOWS
THE THREE MAIN MECHANISMS OF RETENTION IN POROUS MEDIA FLOWS WILL BE ANALYZED: ADSORPTION ON SURFACE, RETENTION DUE TO CHEMICAL REACTIONS AND HYDRODYNAMIC RETENTION. THE LEVELS OF RETENTION IN POROUS MEDIA FLOWS WILL BE COMPARED TO THOSE OBTAINED IN BATCH EXPERIMENTS USING THE POWDER COMING FROM FLOWS WILL BE COMPARED TO THOSE OBTAINED IN BATCH EXPERIMENTS USING THE POWDER COMING FROM DESAGGREGATION OF THE POROUS MEDIA. THE EFFECTS OF DESORPTION AND OF POLYDISPERSITY LEADING TO ADSORPTION CHROMATOGRAPHY WILL BE INVESTIGATED. KINETICS ASPECTS WILL BE TESTED BY PERFORMING EXPERIMENTS AT DIFFERENT FLOW RATES. THE EFFECTS OF CHEMICAL REACTIONS LIKE ION EXCHANGES, DISSOLUTION AND PRECIPITATION LEADING TO SUPER MACROMOLECULAR AGGREGATES (MICROGELS) WILL BE INVESTIGATED USING POROUS MEDIA WITH COMPLEX MINERALOGY, SUCH AS MIXTURES OF SAND, CLAY AND CARBONATES. THE DIFFERENT TYPES OF HYDRODYNAMIC RETENTION WILL BE ANALYZED AND MODELLED.
PHASE 4: MECHANICAL DEGRADATION
THE PHENOMENON WILL BE STUDIED IN MODEL POROUS MEDIA, ADSORBENT AND NON ADSORBENT AND A METHODOLOGY FOR DETERMINING THIS DEGRADATION WILL BE ESTABLISHED. MECHANICAL DEGRADATION WILL BE RELATED TO RHEOLOGICAL CHARACTERIZATION OF THE SOLUTIONS.