Study On Micro-residual Oil Distribution Of Low Permeability Sandstone Reservoir In Upper Es4 Of Chunhua Oilfield

At present,58% of the unexplored oil geological reserves in China are low permeability sandstone reservoirs,which shows that in the following years,low permeability reservoirs will become an important resource for increasing oil and gas production.At present,most China's oil fields have reached the stage containing high percent of water.Especially in the old oil fields in eastern part,the water content is generally more than 90%.The remaining oil tapping potential and comprehensive adjustment have become the main topics for oil fields to maintain the production.Therefore,the study of oil distribution and formation mechanism is of great significance.Based on reservoir characteristics,the experiments of columnar core water flooding and microscopic simulation model were carried out.Then the distribution law of micro-residual oil and forming mechanism were analyzed.The results show that the remaining oil distribution of the two experiments are consistent.The remaining oil can be classified into six types: pore-cavity filling,semi-filling,throat retention type,pore wall,corner and dispersed oil droplet.Pore-cavity filling and semi-filling types are the most important residual oil distribution pattern in low permeability reservoir.The micro-displacement experiments show that the residual oil type after the water flooding in the unfilled fracturing model is semi-filling type,which is mainly related to the poor micro-pore structure and the strong heterogeneity.The simple crack corrosion model has a significant decrease in the throat retention residual oil type;the pore-throat type and the corner-type residual oil are mainly increased.This is mainly due to the serious flow through the mainstream transport channel.In mesh crack corrosion model,pore throat filled residual oil has a significant reduction,which is mainly related to the formation of the mesh cracks after the fracturing,the increasing displacement range of the displacement liquid,and the reduction of the distribution area around the flow zone.In the three models,the reticulosic model has the highest oil displacement efficiency,followed by the simple fracture model and the unfractured model.The mechanisms of the remaining oil formation are capillary closed role,the hole within the displacement of the role of the liquid,the hole within the role of liquid replacement effect,corner capture.