| The low permeability reservoir is the important resource base of increase in oil reserve and production in this21st century and even in the future. It is even more, a low permeability fractured reservoir is the field which needs more key technology research. PGL block C6reservoir is a typical "3lows" reservoir with artificial fracturing fracture and micro fracture development. This C6reservoir water drive reserves produced degree is very low and oil production stable is difficult, because the heterogeneity of inner layer and interlayer is strong the salinity of stratum-water is high and the injection water along high permeable zones dart fast. Polymer/surfactant flooding technology is a method to display fully the polymer and surfactant with their respective advantages and synergies to enhance oil recovery. At present, the technology is mainly used for sandstone reservoir in low temperature and low salinity. The sandstone reservoir’s permeability is greater than50mD and has a medium heterogeneity. This paper uses the methods of experimental research to identify whether the technology has a flooding and blocking effect on PGL block of extra low permeability fractured reservoir and whether to achieve purpose of enhancing oil recovery.Firstly, this paper has expounded the general characteristics, seepage characteristics and development characteristics of extra low permeability fractured reservoir.Then it has researched and summarized the S/P flooding examples and the present development situation at home and abroad. It also has summarized the current development situation of physical simulation technology. Secondly, The geologic development characteristics of PGL block have been analyzed, especially the crack’s situation of PGL block was analyzed in the paper. Finally, this paper has put forward the problems existing in the development.It also has a preliminary discuss in adaptability of Polymer/Surfactant flooding technology in the target reservoir.It has refined the formula problems which need to be solved.This paper mainly gets the optimization and evaluation method for P/S system formula through the experiment. And chose one S/P formula from4kinds of polymer and4kinds of surfactants, which is suitable for the target reservoir. There are some polymer performance which need to be emphasized on, they are:improving oil displacement efficiency characteristics, injection pressure, aging stability, salt resistance properties, shear properties, adsorption, a matching relationship with the pore throat, etc. There are some surfactant performance which need to be emphasized on, they are, reducing the interfacial tension properties, adsorption, etc. Mix X4polymer of2000mg/L and Y1petroleum sulfonate surfactants of1500mg/L which has been chosed, and then evaluate the performance of S/P system.These studies indicate that, The S/P system which has been chosed has strong adaptability in the low permeability fractured reservoir of PGL block.①The moderate injection pressure can reduce the influence of the Low Speed non-Darcy seepage, improve the tonguing phenomenon so that it is helpful to be used in low permeability field.②It has good salt resistance, shearing resistance, aging resistance and lower adsorption.③It is matching the matrix porosity. Three indoor physical simulation experiments of small core diameter(2.5cm) oil displacement for comparison have been made to the polymer flooding, surfactant flooding and S/P flooding.Finally, we take natural outcrop from mine and make the3D physical model according to the principle of similar, design the core parallel experiment scheme of3D model, use the patent of our laboratory equipment and high temperature and high pressure3D physical model of large scale to do displacement experiments. According to the analysis of experimental results, the S/P flooding in PGL block of extra low permeability fractured reservoir is feasibile and it can improve the recovery by6.5%. |
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