Study On Nonlinear Seepage Law Of Low Permeability Sandstone Reservoir

The proved unutilized low permeability reservoirs in Jidong Oilfield are very large,it has the characteristics of poor physical property and great difficulty in development.Because the understanding of low permeability reservoir and fluid characteristics is not thorough,the nonlinear seepage model is urgently needed in the same time.In this thesis,through experiments,model derivation and other aspects of study,on the basis of starting pressure gradient experiment and boundary layer flow experiment,combined with the mechanism of nonlinear seepage,the nonlinear seepage model of low permeability reservoir in Jidong Oilfield is constructed,and the nonlinear seepage law of low permeability block in Jidong Oilfield is deeply analyzed.The main achievements are as follows:(1)Based on the actual situation of the study block,the main influencing factors of nonlinear seepage are analyzed.The main factors affecting the nonlinear seepage law of Jidong Oilfield are porous media,fluid characteristics,and the interaction between porous media and fluid.(2)On the basis of the starting pressure gradient experiment of single-phase and multi-phase fluids,a new empirical formula of starting pressure gradient is obtained,forming the starting pressure gradient chart of different fluids.For cores below 1m D,the starting pressure gradient of water phase increases with the decrease of permeability.At the same time,when the minimum starting pressure gradient increases,the increase range of the proposed starting pressure gradient decreases.(3)Under the premise of the boundary layer flow experiment,the influencing factors of boundary layer are obtained.The main influencing factors are average pore throat radius,viscosity and pressure gradient.The empirical formula for quantitative characterization of boundary layer thickness is established,and the error is 13.3%compared with experimental data.(4)Based on nonlinear seepage theory,starting pressure gradient experiment and boundary layer experiment,the influence of starting pressure gradient and boundary layer thickness on reservoir seepage law are comprehensively considered,and a new fractal model of nonlinear seepage for reservoir characteristics is established.