Study On Main Factors And Principles During Imbibition Procession In Ultra-low Permeability Reservoirs

The ultra-low permeability reservoirs,which are featured by low permeability,small porosity and poor flow environment because of the boundary layer in the pore throat,are often developed with stimulated fractured method so that complex fracture network exists in the formation.Then the imbibition will happens between the water in fractures and the oil in matrix rock because of the capillary force,so that the crude oil in matrix is replaced by water.Therefore,imbibition is regarded as an important seepage mechanism,of which the study is of great significance.But the specific imbibition law of ultra-low permeability reservoirs is not clear by now.Based on the above problem,we have made the following research:(1)the influence of matrix length,matrix permeability and matrix-fracture condition on imbibition is studied at first by means of imbibition experiments,within which the laws of imbibition recovery and imbibition velocity are obtained;the corresponding imbibition law,as well as the main factors of imbibition under the core scale,has been gotten;(2)based on the existing expression of the boundary layer;in combination of the heterogeneous or homogeneous capillary-bundle model,the capillary imbibition phenomenon is studied with or without considering the boundary layer,thus the main factors of the imbibition under the microscopic scale are clarified and a new capillary formula is set up;(3)a new calculation method of radial boundary element method has been applied in the imbibition mathematic model,of which capillary parameter has been revised,in the mine case calculations;the results shows imbibition in the water injection process will slow down the advancing of the waterline and improve the oil recovery.In this paper,we reveal the mechanisms of capillary imbibition of ultra-low permeability reservoirs,set up a new capillary expression and put forward a more practical imbibition mathematical model.The results of this essay have certain guiding significance to understand the law of imbibition in ultra-low permeability reservoir and guide the development of ultra-low permeability reservoir.