THE AIM OF THIS PROJECT IS TO SET UP A NUMBER OF CHEMICAL SYSTEMS CAPABLE OF PLUGGING THE DRAINING PATHS AT THE CORE OF OIL RESERVOIRS IN ORDER TO FORCE THE INJECTED WATER TO SWEEP THE LESS POROUS RESERVOIR ROCKS THUS INCREASING THE OIL RECOVERY EFFICIENCY.
A major effort is underway in the petroleum industry to understand the role of heterogeneities and to improve the oil recovery process through a better management of the flux of water and oil in a given reservoir. Modifying the profiles of water injection is an essential part of this strategy. Gels and foams are the most commonly considered. Little is known on the behaviour of these agents in nonfractured porous media. Research was performed on the systems which are considered by the profession to be of a major interest to better understand their behaviour in actual formation rocks, test their long term stability and try to extend their use to zones further from injection wells and to harder environments.
The work centred on gels formed by polymers physically crosslinked by chromium cations. Covalent gels were also considered, as well as plugging agents obtained by precipitation and foams. The main conclusion was that polymer chromium gels are confined to the wellbore even in clean environments. Several attempts were made to improve product propagation but none of them worked.
Other systems have shown a good ability to penetrate and to plug deeper into the formations but penetration would still be at a limited distance and a large quantity of product is required making the operations rather costly.
An optical technique was proposed for foaming agent as it has been shown that optimal foam quality for permeability reduction does not depend on injection rate, but much work remains to be done on foam efficiency.
THE EFFICIENCY OF THE SECONDARY OIL RECOVERY FROM FRACTURED ROCK RESERVOIRS BY WATER INJECTION IS OFTEN POOR. SLOWING DOWN OR STOPPING THE WATER ADVANCING INTO THE MORE PERMEABLE AREAS WOULD FORCE IT TO SWEEP THE LESS PERMEABLE ONES THUS ENHANCING THE OIL RECOVERY EFFICIENCY. THE INTENTION IS TO SET UP A TECHNIQUE WHICH UNLIKE THE CONVENTIONAL ONES, WILL ALLOW THE DRAIN PATHS TO BE PLUGGED AT THE CORE OF THE RESERVOIR IN SPITE OF THE PREVAILING HIGH TEMPERATURES (150 CELSIUS DEGREES) AND SALT CONTENT. THIS REQUIRES: A DELAYED EFFECT OF THE PLUGGING AGENT, A LONG ENOUGH DURABILITY OF THE PLUGGING AS WELL AS ITS POSSIBLE REVERSIBILITY.
THREE CLASSES OF PLUGGING AGENTS WILL BE EXAMINED, EACH SUITED TO DIFFERENT RESERVOIR CONDITIONS AS TO TEMPERATURE, PRESSURE, PH, AQUIFER ACTIVITY ETC... NAMELY; GELS (SILICATES), CROSSLINKED POLYMERS AND FOAMS.
THE SEARCH FOR THE BEST DIVERTING AGENTS WILL BE MADE AMONG GELS BY TAKING INTO ACCOUNT A NUMBER OF PROPERTIES, LIKE THE RESISTANCE TO EXTRUSION, THE SHRINKING CAPACITY IN THE LONG TERM , THE PERMEABILITY TO WATER AND OIL, THE BIODEGRADATION ETC...
THE PARAMETERS BRINGING ABOUT THE DELAYED PLUGGING EFFECT (CROSSLINKING, HYDROLYSIS) WILL BE CAREFULLY EXAMINED. FOR THE FOAMS, THE CHOICE WILL BE BASED ON THEIR STABILITY. AFTER A FEW TESTS WITH THE SINGLE REACTANTS, AIMED AT STUDYING THEIR TRANPORT PHENOMENA, THE EFFICIENCY TESTS OF THE PROPOSED CHEMICAL SYSTEMS WILL BE MADE ONTO PHYSICAL MODELS REPRODUCING TYPICAL RESERVOIR SITUATIONS (FRACTURED ROCKS, POROUS SYSTEMS) AT TEMPERATURES UP TO 150 DEGREES CELSIUS BOTH IN THE ABSENCE AND IN THE PRESENCE OF AN OIL PHASE. THE FLOW LAWS OF THE ASSOCIATED CHEMICAL COMPONENTS BEFORE THEIR INTERACTIONS SHALL FIRST BE OBTAINED AND THE BEST WAY OF DELAYING THEIR REACTION AFTER INJECTION WILL BE SOUGHT. THE GELATION WHEN THE SYSTEM THICKENS WILL THEN BE MONITORED AND DESCRIBED. AN ATTEMPT WILL BE MADE TO CHARACTERIZE THE GELS AS TO THEIR RESISTANCE TO DISPLACEMENT UNDER INCREASING PRESSURE GRADIENT AND TO OIL PERMEABILITY. THEIR LONG TERM (SEVERAL MONTHS) EVOLUTION IN THE POROUS MEDIUM WILL BE MONITORED, ESPECIALLY IF SHRINKING OCCURS. EITHER INTRINSIC (FOAM DRAINAGE, THERMAL DEGRADATION, SHRINKING) OR EXTERNAL MEANS (PRESSURE INCREASE, REACTANT INJECTIONS) CAN BE DEVISED TO DELIBERATLY DESTROY THE SELECTED PLUGGING SYSTEMS. PHENOMENOLOGICAL MODELS FROM LABORATORY EXPERIMENTS WILL BE SET UP AND EXTRAPOLATIONS SHALL BE ATTEMPTED TO 2D OR 3D FIELD-SCALE MODELS.