Enhanced Oil Recovery Mechanisms For Preformed Particle Gel-Surfactant In Fractured Reservoir

During the development of fractured reservoir using water flooding, the injection wateris incline to flow along the fracture, which causes early water breakthrough in the producedwell and watercut increases quickly even serious water out. There are still amount of residualoil left and the recovery is very small. Therefore, the combination of preformed particle geland surfactant was proposed to improve oil recovery in fractured reservoir. The mechanismsof interaction between preformed particle gel and surfactant were discussed. The profilecontrol and leak-off properties were also studied. Then, a discrete-fracture model of thecombination EOR method of preformed particle gel and surfactant was developed. Finally themicroscopic EOR mechanisms of the combination were proposed.A type of preformed particle gel was prepared using solution polymerization method.According to the storage modulus, the synthesis conditions of preformed gel were optimized.The preformed gel was characterized by FTIR spectra. The three dimensional networkstructure of preformed particle gel after swelling was observed by ESEM.The interaction rules of preformed particle gel and different types of surfactants werestudied from adsorption property, interfacial tension, swelling ratio and rheological property.The interaction mechanisms were discussed using SEM and AFM. The interaction forcebetween anionic surfactant and preformed particle gel is electrostatic repulsion at lowconcentration, while the force is hydrophobic association at high concentration. Theinteraction force between nionic surfactant and preformed particle gel is only hydrophobicassociation even at low concentration. The interaction force between cationic surfactant andpreformed particle gel is hydrophobic association and electrostatic attraction.The matching relationship between preformed particle gel and width of fracture, thepropagation rules and the profile control property were studied using fractured model. Then, the leak-off and the damage extent of preformed particle gel were evaluated using hightemperature static loss test. When the ratio of size of preformed particle gel to width offracture is less than four, the particle can pass through the fracture by direct passing through,deformation or breakage to indepth the fracture; while when the ratio is more than four, theparticle can not pass through the fracture but directly plug the fracture at the inlet. Therelationship of injection pressure and resistance factor of preformed particle gel in fracturewith the injection rate follows power-law model. The injectivity and propagation ofpreformed particle gel become better while the plugging ability become worse in the presenceof surfactant. Preformed particle gel has selective profile control ability to oil and water aswell as high permeable layer. The leak-off maily occurs near the wellbore. The filter formedby leakoff prevents the injection water from entering into the matrix. But if the filter isremoved, the permeability of the matrix can recover again.The physical simulation flooding experiments of preformed particle gel and surfactantsystem were conducted using fracture core and the EOR ability was evaluated. The resultsshows that this combination system can significantly improve oil recovery in fracturedreservoir and the EOR effect can become better if the carring medium is HPAM solution. Themicroscopic flooding experiments shows the EOR mechanisms that includes selective profilecontrol, indepth fluid divertion after propagation, displacement oil by deformation of particlegel and surfactant flooding mechanism.Based on the physical simulation results, a disceret fracture model was developed for thepreformed particle gel and surfactant. The flow model was resolved using ComsolMultiphysics software on the basis of concept formation model. The effect of parameters suchas slug composition, slug size, preformed particle gel concentration, surfactant concentration,injection rate, and injection time on the recovery was discussed.