Study On Identifying And Charactering The Thief Zones Of Layered Reservoirs

Waterflooding is the most economical and effective way in most oilfields.However,most of the oilfields have entered the middle and late stages of development,and are located in the high water-cut or ultra-high water-cut development stage with serious invalid cycled water.Making clear the connection between injection and production wells and understanding the flow of the injected water have a very important significance.At present,most of the models for inverting the dynamic connectivity between wells are single-layer models.However,most oilfields in the site have many small layers.Due to the economic,geological and technical conditions,not all wells in each layer have complete production data,which adds the difficulty of the application of the model to the real oil field.As a result,the true situation of the formation can not be accurately and completely reversed.In order to better reflect the connectivity between injection and production wells in multilayer reservoirs,this paper establishes a multi-layer dynamic connectivity model based on material balance and superposition principle.Taking into account the incomplete monitoring data and shut-down wells and other issues,the model is improved accordingly.With the objective of minimization of the squared sum of the actual fluid production and fluid production calculated by the model,improved simulated annealing particle swarm optimization algorithm is used to solve the model.And the model is validated by time constants and typical reservoirs.The minimum input data points of model is also determined by the asymmetric coefficient of multi-layer reservoir proposed.By the coefficient of variation of coefficient of communication and coefficient of water absorption proposed,based on the theory of probability and statistics,the clustering analysis algorithm is used to establish the thief zone classification method,and calculates the permeability,volume and throat radius of the thief zone by using the seepage mechanics theory.The results of mine application show that the improved multi-layer dynamic connectivity model can use production data to invert the connectivity coefficient of each layer,classify and parameterize the thief zone.The method is simple,practical and accurate.The result is consistent with the on-site monitoring data.