Development of New Oil Recovery Process Controlling Formation of Polymer Gel in Reservoirs

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CAG (COィイD22ィエD2-Water Alternating Gelant Injection Process) is proposed as a new scheme of in-situ polymer gelation in reservoirs. It is comprised of alternate injection of the two solutions : saturated aqueous carbon dioxide and gelant (aqueous solution of polyacrylamide, NaAlOィイD22ィエD2 and NaOH).To design and evaluate the CAG laboratory experiments were performed. The optimum concentrations of polyacrylamide, NaAlOィイD22ィエD2 and NaOH in gelant were selected from beaker tests. The experiments using glass-bead packed cores revealed that the CAG was able to form gel and reduce the core permeability by about 1/60 to 1/360 of its original permeability. Flood experiments with linear cores and with two linear cores of different permeabilities mounted in parallel showed that the CAG was also effective to increasing oil recovery. Two-dimensional models packed with glass beads were built to investigate the effect of crossflow between layers on the CAG. The control of gel placement was found to be difficult when strong crossflow existed. An appropriate injection scheme considering the permeability ratio must be selected when the CAG is applied to reservoirs consisting of different-permeability layers.Regarding to modeling study, a numerical model was developed for predicting flow behavior accompanying gel formation in porous media. The model calculations were able to reproduce the experimental results by matching the rate constant of gel formation.The proposed CAG is a simple and promising method to recover remaining oil from matured reservoirs. The further study on injection scheme to control gel formation is recommended for its field application.