Abstract
This paper deals with a new method used to describe the present permeability of reservoir theoretically and its application in profile control and water shutoff. The reservoir permeability has been changed greatly compared with the initial stage of development after long time water flooding. Generally speaking, it is very hard to obtain the current reservoir permeability data. Only the native permeability, which has great diversity with the actual reservoir conditions, can be considered in profile modification. So a lot of problems usually exist in the process program designed according to the native permeability data. It doesn't conform to the actual conditions of current reservoir. So the expected result is hardly obtained after field implementation according to project design. In such cases a good predictor is necessary, requiring more rigorous models capable of adequately handling any inherent non-linearity. Genetic algorithm is a new intelligent computing method, based on which the technology of permeability prediction is developed. The approach adopted here allowed us to integrate the theory of survival of the fittest into our geologic understanding of the reservoir to look for the permeability distribution that is closest to the actual reservoir conditions by using the three operators of selection, crossover and mutation repeatedly. Using genetic algorithm, we have established a relationship between permeability and field production datas that are available. These datas include bottom hole flowing pressure, production rate, waterflood injection rate and water cut etc of test field. This technology is suitable for well pattern or fault-block with balanced injection and production. According to the relative accurate and reliable permeability distribution, the blindness of profile modification project design can be avoided. Accordingly the implementation result can be improved greatly, and can obtain good evaluation by using this technology again after implementation.
This technology has been applied successfully in L58-2 Fault-Block of Linpan Oilfield, M12 Fault-Block of Qinghe Oilfield, M14 Fault-Block of Qinghe Oilfield and Feiyantan Oilfield before and after profile modification to predict their present permeability distributions and evaluate implementation results. The predicted results basically accorded with the performance results analyzed by field technicians, which had led to an enhanced reservoir characterization and decreased reservoir heterogeneity. This benefits both daily operations and reservoir stimulation efforts. This technology will be popularized in Gudao, Gudong Oil Field. With further development and improvement, it will play more and more important role in profile modification, water shutoff and enhanced oil recovery in heterogeneous reservoir.
