Research On Non-Linear Flow Characteristics Of Ultra-low Permeability Reservoir And Application Of Gas-Water Alternate Flooding

The formation seepage ability of ultra-low permeability reservoirs is weak and it is difficult to complement formation energy.Gas-water alternately flooding taking into account the characteristics of secondary and tertiary oil recovery is a technical means that can effectively supplement the formation energy.Because ultra-low permeability reservoirs have significant nonlinear seepage characteristics,it is of great significance to conduct research on the nonlinear seepage characteristics and pressure propagation mechanism of the reservoirs,and the pressure propagation and parameter design of gas-water alternation flooding in ultra-low permeability reservoirs.Based on the sedimentary facies and the connection characteristics of reservoirs,the geological and reservoir characteristics of the study area are described,and the reservoir heterogeneity and original oil-water distribution characteristics are analyzed.The starting pressure gradient experiment of ultra-low permeability reservoir in the study area was carried out based on unsteady state method.Based on the distribution characteristics of the pressure gradient between injection and production wells,the unstable seepage flow was analyzed using the integration method and the steady-state sequential replacement method.The effective injection-production well spacing under the condition of pseudo-stable seepage flow in ultra-low permeability reservoirs is evaluated.Based on the long core displacement model,experiments of gas-water alternating pressure conduction and parameter optimization are carried out.Based on the numerical model,orthogonal experiments are used.the influence degree of injection parameters and the design of injection scheme were carried out.The characteristics of water injection development in the study area were evaluated,and field effect analysis was carried out.The research results show that:the heterogeneity in the study area is weak,and various features are suitable for the alternate development of gas and water;the fitting results of the starting pressure gradient experiment show that the starting pressure gradient in the study area is about 0.0237MPa/m;the starting pressure gradient increases nonlinear,At the same time,it expands the difference in oil-water pressure wave propagation under unstable conditions;it can maintain a reasonable propulsion speed during gas-water alternation and prolong the pressure release time.Compared with oil flooding and water flooding under experimental conditions,the core after the gas-water alternation scheme,Natural pressure relief,pressure wave propagation time increased by 14.92min and 26.96min,respectively;The parameter optimization experiment shows that properly increasing the injection intensity and the earlier injection is conducive to improving the development effect,and there is an optimal value for slug size and gas-water ratio.If the slug size is too small,the injection difficulty is increased,and the gas-water ratio is prone to gas channeling.;Based on the orthogonal experiment,the on-site optimal parameter combination scheme is:gas-to-water ratio3:1,injection rate14m~3/d,alternating period 40d,injection timing(water content)40%.After implementing gas-water alternation for the study area for one year,the average water content decreased by 11.2%,and the number of wells with stable production increased to 96%of the total wells.Gas-water alternation flooding has a significant effect of precipitation and oil increase in the study area.